The present invention relates to a wet film applicator which is manually moved across a surface to cause a flowable substance to be spread in the form of a thin film across the surface.
Wet film applicators of that type are employed in the testing of substances such as paint for example, for particular characteristics such as color, opacity, gloss, flexibility, toughness, ratio power (hiding power), weatherability, chemical resistance, etc. It is important that the thickness or depth of the test film be consistent from one film-spreading operation to the next so that proper comparisons can be made. In certain tests, it is also necessary that the film thickness be uniform, whereas in other tests, it is necessary that the thickness be non-uniform, i.e., a so-called wedge-shaped film. A wedge-shaped film is useful, for example, in testing hiding power of a substance, because the depth at which the film is able to cover an underlying pattern can be discerned.
Various types of wet film applicators have been conventionally utilized. For example, so called "fixed-gate" applicators comprise two side walls and a transverse blade rigidly interconnecting the side walls. The area bordered by the side walls and blade defines a reservoir disposed ahead of the blade for confining a pool of a flowable substance to be tested. The lower, beveled edge of the blade is spaced above the lower edges of the side plates to define a clearance between the blade edge and the surface. Thus, when the applicator is moved in a forward direction of movement, the flowable substance is spread by the blade to a thickness controlled by the clearance.
It is desirable that the height of the clearance be varied by raising or lowering the blade, whereby a so-called adjustable clearance type of applicator can be employed. Such adjustment might be made in some applicators by inserting or removing shims between the blade and side walls. In other applicators, the blade can be raised or lowered by actuation of micrometer screws which extend through a top rail overlying the blade. In still another applicator, the blade can be adjustably slid along a pair of parallel runners having inclined faces; the runners are mounted on a one-piece block (i.e., are rigidly interconnected), and the blade is held in positions of adjustment by a set screw.
It has also been proposed to provide a blade which is stepped along its length to define blade sections of different clearance. Such a blade could, for example, be utilized to spread a film in the form of strips of different thickness. When such a film is spread over a pattern of lines, the coating thickness for complete opacity can be determined by observing which film strip just hides the lines.
As a variation of the above-described stepped blade, the blade edge may be inclined from one side wall to the other so as to define a continuously varying clearance. Such an arrangement creates the wedge-shaped film discussed earlier, and thereby defines a larger number of clearances as compared to a stepped blade. However, the clearances which can be tested are limited to the particular inclination of the blade edge which is usually fixed.
It would be desirable to provide an applicator which is of simplified construction and yet capable of providing films of uniform thickness and non-uniform thickness, and which provides a blade height adjustment feature in connection with both types of film.